Tap water is improved by filtering it and it has a noticeable effect when brewing it. Alternatively you could collect water from mountain streams (if you happen to have any in your area) from time to time.

Thanks for the suggestions guys!! Been using filtered water and it's given me the best results!

That said, I think I've found the holy grail for bottled water for expensive teas (wouldnt bother buying it for everyday drinking) it's definately been the best in all the ones I've tested, but its all about opinion too I suppose!